A micro gas turbine having a compressor, a generator and a turbine is known from EP 1 564 379 A2. In this known gas turbine, the rotor of the generator comprises a shaft which is journaled in bearings which are part of the generator. The compressor shaft and the turbine shaft are coupled to the generator shaft.
The structural and rotordynamic requirements for the coupling between the generator and the compressor and turbine shafts are high because of the high rotational speed. The shafts also impose specific alignment requirements. They also limit the bearing type choice.
Electric motor assisted turbochargers are known from US 2008/0124233 and from US 2009/025386. These are not micro gas turbines. Yet, they incorporate an electrical machine between a compressor and a turbine. There is one bearing unit between the compressor and the electrical machine and another bearing unit between the turbine and the electrical machine. These known turbochargers imply custom design of the electrical machine, shaft-bearing system, compressor and turbine. This leads to high design, development and manufacturing costs.